1. Field of the Invention
The present invention relates to a multimedia broadcast/multicast broadcast service (MBMS) in a mobile communication system and, more particularly, to discontinuously transmitting and receiving MBMS data between a network and a mobile terminal.
2. Description of the Related Art
The universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from the global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access technologies.
A related art UMTS network structure 1 is illustrated in FIG. 1. A mobile terminal, or user equipment (UE), is connected to a core network (CN) through a UMTS terrestrial radio access network (UTRAN). The UTRAN configures, maintains, and manages a radio access bearer for communications between the UE 2 and the core network to meet end-to-end quality of service requirements.
The UTRAN includes a plurality of radio network subsystems (RNS), each of which comprises one radio network controller (RNC) for a plurality of base stations, or “Node Bs.” The RNC connected to a given base station is the controlling RNC for allocating and managing the common resources provided for any number of UEs operating in one cell. One or more cells exist in one Node B. The controlling RNC controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B may receive an uplink signal from a UE and may transmit downlink signals to the UE. Each Node B serves as an access point enabling a UE to connect to the UTRAN, while an RNC serves as an access point for connecting the corresponding Node Bs to the core network.
Among the radio network subsystems of the UTRAN, the serving RNC is the RNC managing dedicated radio resources for the provision of services to a specific UE and is the access point to the core network for data transfer to the specific UE. All other RNCs connected to the UE are drift RNCs, such that there is only one serving RNC connecting the UE to the core network via the UTRAN. The drift RNCs facilitate the routing of user data and allocate codes as common resources.
The interface between the UE and the UTRAN is realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3) described in, for example 3GPP specifications. These layers are based on the lower three layers of an open system interconnection (OSI) model that is a well-known in the art of communication systems. A related art architecture of the radio interface protocol is illustrated in FIG. 2. As shown, the radio interface protocol is divided horizontally into the physical layer, the data link layer, and the network layer, and is divided vertically into a user plane for carrying data traffic such as voice signals and Internet protocol packet transmissions and a control plane for carrying control information for the maintenance and management off the interface.
The physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the MAC layer and the physical layer via a transport channel. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (transmitter).
The MAC layer of the second layer provides a service to an upper layer of a radio link control (RLC) layer through a logical channel. The RLC layer provides support for reliable data transmissions, and may perform a function of segmentation and concatenation of an RLC service data unit (SDU) coming from an upper layer.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane and controls transport channels and physical channels with respect to the establishment, re-establishment, and releasing of radio bearers. A radio bearer (RB) is a service provided by a lower layer, such as the RLC layer or the MAC layer, for transferring data between the UE and the UTRAN and guaranteeing a predetermined quality of service between the UE and the UTRAN.
The establishment of an RB determines regulating characteristics of the protocol layer and channel needed to provide a specific service, thereby establishing the parameters and operational methods of the service. When a connection is established to allow transmission between an RRC layer of a specific UE and an RRC layer of the UTRAN, the UE is said to be in the RRC-connected state. Without such connection, the UE is in an idle state.
A UTRAN RRC layer requests one or more measurements from a terminal (UE) RRC in order to control a radio bearer. For example, the UTRAN RRC layer requests the UE RRC to measure power of a channel transmitted in a specific cell or to measure power of a channel transmitted from a specific frequency.
Hereafter, a Multimedia Broadcast/Multicast Service (MBMS or “MBMS service”) will be described. MBMS refers to a method of providing streaming or background services to a plurality of UEs using an MBMS radio bearer that utilizes at least one of point-to-multipoint and point-to-point radio bearers. One MBMS service includes one or more sessions and MBMS data is transmitted to the plurality of terminals through the MBMS radio bearer only while the session is ongoing. Here, a session is a time period during which particular data is sent by the network.
As the name implies, an MBMS may be carried out in a broadcast mode or a multicast mode. The broadcast mode is for transmitting multimedia data to all UEs within a broadcast area, for example the domain where the broadcast is available. The multicast mode is for transmitting multimedia data to a specific UE group within a multicast area, for example the domain where the multicast service is available.
The UTRAN provides the MBMS service to a plurality of UEs by using the RB. RBs used by the UTRAN can be classified as a point-to-point RB or a point-to-multipoint RB. The point-to-point RB is a bi-directional RB, including a logical channel DTCH (Dedicated Traffic Channel), a transport channel DCH (Dedicated Channel) and a physical channel DPCH (Dedicated Physical Channel). Alternatively, the point-to-point RB may include the DTCH, a transport channel FACH (Forward Access Channel) and a physical channel SCCPCH (Secondary Common Control Physical Channel).
The point-to-multipoint RB is a uni-directional downlink RB, including a logical channel MTCH (MBMS Traffic Channel), a transport channel FACH (Forward Access Channel), and the physical channel SCCPCH. The logical channel MTCH is configured for each MBMS service provided to one cell and is used to transmit user plane data of a specific MBMS service to the UEs.
The UTRAN providing the MBMS service transmits a control message, namely, an MBMS-related RRC message to the plurality of terminals (UEs) through an MCCH (MBMS Control Channel). The MBMS-related control message includes a message providing MBMS service information and a message providing point-to-multipoint RB information. As shown in FIG. 3, the logical channel MCCH is the point-to-multipoint downlink channel and is mapped to the FACH, which is mapped to the SCCPCH. Only one MCCH exists in one cell.
Accordingly, when a terminal wants to receive a specific MBMS service using the point-to-multipoint RB, it receives an RRC message including RB information through the MCCH and sets a point-to-multipoint RB using the RB information. After the point-to-multipoint RB is set, the terminal continuously receives a physical channel SCCPCH, to which an MTCH is mapped, to obtain specific MBMS service data transmitted through the MTCH.
However, in the related art, because the terminal cannot recognize when the MBMS data is transmitted through the MTCH during a session, i.e., the exact MBMS data transmission time, the terminal must continuously receive the SCCPCH to which the MTCH is mapped during the session. Thus, the terminal is unable to perform other operations such as measuring a channel of a different cell during the session. In addition, when the terminal does perform the measurement operation, it cannot receive the MBMS data transmitted during the measurement operation.